RELATING TO SECONDARY SEXUAL CHARACTERS. 29 



When the father is Wyandotte, the daughters are like him (except for 

 stippling of the Leghorn type). When the father is Brown Leghorn 

 the daughters are somewhat stippled red birds. In the former case 

 the daughters getting their Z chromosome from their Wyandotte 

 father resemble him; in the latter case the daughters getting their Z 

 chromosome from their Leghorn father look more like him. Their 

 failure to look exactly like him must be due to autosomal factors 

 derived from the Wyandotte mother that dominate other autosomal 

 factors from the father. 



Hagedoorn crossed Black Breasted Game bantams (like those used 

 in my Sebright crosses) to Brown-Breasted bantams. In the latter 

 the black breast feathers of the male are bordered by lemon ; the hens 

 are nearly black. Black-breasted male to "brown-red" female gave 

 both black-breasted sons and daughters. In the reciprocal cross all 

 the sons were black-breasted (like the mother) and all the daughters 

 were brown red like the father. Evidently the factor here for Brown 

 Breasted game is sex-linked and recessive. In this case the new 

 mutant sex-linked character is recessive to the wild type. 



Davenport (1912) crossed Brown Leghorns to Dark Brahmas. In 

 the cross and its reciprocal all the sons are alike. Two dominant sex- 

 linked factors were found, 1 viz, the white background characteristic of 

 the Dark Brahmas and the red upper wing-coverts (and back) charac- 

 teristic of the Brown Leghorns. On the other hand, the daughters 

 differ in the two crosses, in each case resembling their father in their 

 hackle color. 



When two sex-linked characters are involved in a cross it is possible 

 to determine by suitable matings whether an interchange between the 

 chromosomes that bear them has taken place. In the case of the sex 

 chromosomes only one sex, the male, has both like chromosomes, viz, 

 ZZ, and we expect from analogy with the Drosophila work that 

 crossing-over would be found between the sex chromosomes only in 

 the male. Goodale has recently (1917) made the important discovery 

 that in poultry crossing-over takes place between the sex chromosomes 

 (ZZ) in the male, but not in the female (ZW or ZO). This relation, 

 therefore, is the reverse in birds and flies, for, in the one, crossing- 

 over takes place in the female and in the other in the male. Whether 

 this difference extends also to the other chromosomes in birds as it 

 does in flies is as yet not known. 



Several years ago some crosses between gold and silver Campines 

 were reported by Rev. E. Lewis Jones. The results are consistent with 

 the view that a sex-linked factor pair is responsible for this difference 

 in color, although the author does not apply this view to his results. 

 The results may be seen in the table on page 16, to which Jones has 



1 One may be either sex-linked or sex-limited so far as the evidence goes. 



